Does Fish Have White And Dark Meat?

If you've ever carved a turkey for Thanksgiving or picked apart a rotisserie chicken from the supermarket, you know the difference between white meat and dark meat. White meat comes from the breast of the bird, and is generally mild in flavor and dry in texture; dark meat, on the other hand, comes from the legs, wings, and thighs of the bird, and is juicier and more rich in flavor. The division comes from the presence of slow oxidative muscle fibers in parts of the body, like the legs and thighs, that get exercised more often; their high levels of myoglobin, an iron-rich protein, make the flesh darker in color.

But what does this mean for fish? After all, fish come in a wide variety of colors, from the mild white flesh of cod or haddock that you'll find in fast food sandwiches to the rich, steaky pink of the tuna or salmon in your sushi. (Just be careful with the soy sauce.) Are those differences in color because of myoglobin, as well? The answer: for the most part, yeah!

Just like with chicken (or "tuna of the land", if you prefer), myoglobin concentrates in the parts of a fish that get the most exercise, turning their flesh a shade of red. The difference is that most fish, unlike chickens, don't exert themselves too much. They float through water instead of running or crawling, which is much less strenuous on the body. This is why you'll find many elderly people who take water aerobics classes, and considerably fewer who do CrossFit.

Accordingly, most fish have white flesh aside from their fins and tails, which are used to help them steer through the water. The exceptions are fish like tuna, which require more oxygen so they can swim for longer distances. They get more myoglobin throughout their body, and as such have that characteristic red flesh. This is, essentially, all dark meat: parts of the body that are continuously used and develop tougher muscle, in contrast to the short-burst muscles of white meat.

Myoglobin plays a major role in coloring the flesh of fish, but it is by no means the only determinant. Take salmon, for example: that lovely pink color doesn't necessarily come from continuous exercise, no matter how bravely they swim upstream. No, their color comes from a diet of shrimp and krill. These little crustaceans are rich in carotenoids, which are a kind of antioxidant, that color the flesh depending on how much the salmon eats. For instance, sockeye salmon eat a ton of carotenoid-rich krill, meaning that they have much pinker flesh than coho or chinook salmon, which prefer to eat small fish.

Some swordfish also favor a shrimp-heavy diet, which turns their flesh from a mild white to a vivid orange. These are called "pumpkin swordfish", and they tend to sell for a much higher price than normal swordfish, even though they may or may not taste especially different from each other.